Graduated scale indicator, such as may be used as tuning scales for radio receivers



April 10, 1945. c, s, cocK 2,373,l6$

GRADUATED SCALE INDICATOR, sucn AS MAY BE usso AS TUNING SCALES FOR RADIO-RECEIVERS Filed Aug. 8, 1942 9 10 If 12/! I4 7516 I7 78 19 20 ILL - INVENTOR akratgpfiegfibuyfiocfierell (MM ATTORNEY Patented Apr. 10, 1945 2,373,168

GRADUATED SCALE INDICATOR, SUCH AS MAY BE USED AS TUNING SCALES FOR- RADIO RECEIVERS Christopher Sydney Cockerell, Chelmsford, England, assignor to Radio Corporation of America, a corporation of Delaware Application August 8, 1942, Serial No. 454,154 In Great Britain August 12, 1941 2 Claimsn (Cl. 116-124.1)

The present invention relates to graduated scale indicators, such as may be used as tuning scales for radio receivers, though it should be appreciated that the invention may be used in conturns on a disc, so that it appears as'a plurality of parallel lines in the window an additional travelling ointer may be provided to indicate on which of these parallel lines a reading is to be nection with other apparatus wherein it may be 5 made.

found useful. For convenience, the invention will The correction curve is obtained by calibrating be described as for use with the tuning of radio the receiver at a suitable number of selected receivers. points on the scale.

In modern radio-receivers of high discrimina- The axis by which the graduated cylinder disc tion closely graduated scales of considerable or band is set in motion will usually r q ire to e length may be provided so that the frequency connected to the axis of the tuning element to which the receiver may be tuned may be inthrough a gear train so that it may make several dicated to a high degree of precision. Such scales turns to one turn of the latter. may be provided helically on a cylinder, spirally The invention is illustrated, by way of example on a disc, or obliquely and rectilinearly on a band, in the accompanying drawing wherein Figs. 1 to the member carrying the graduated scale being 3 disclose a particular embodiment, Fig. 1 showso mounted that as the scale-bearing member ing the scale inscribed on a cylinder, Fig. 2 showpasses through a, viewing window, the graduated ing the transparent cover plate that is adapted to scale moves relatively to a cursor line, both across be positioned in front of the cylinder, and Fig. 3 the cursor line and along the length of the showing the assembly of Figs. 1 and 2 behind a cursor line. The graduation of the scale is efwindow in a panel; and Fig. 4 discloses an emfected in accordance with a known law. bodiment of the invention adapted for use in a Where such receivers are required in large multi-band receiver. quantities it is not commercially practicable to In the embodiment of Figs. 1 to 3 the graducalibrate each scale individually and there is, ated scale s is engraven, or otherwise marked in therefore, a definite maximum length of scale accordance with a known law, helically upon a which can be usefully employed for any given cylinder 0 mounted, for rotation about its axis a, set of tolerances of the components which go to adjacent to a window w of a length substantially make up the receiver. Using commercial tolerequal to the length of that part of the cylinder ances for the components the discrimination of over which the helix extends. The line on the such a scale leaves much to be desired, and therecylinder thus presents the appearance of a plufore it is necessary to provide a correction to the rality of short parallel lines extending across the indications given by a scale of such a length as width of the window and set obliquely to the to give adequate discrimination. shortest line across the width. Rotation of the According to the invention a graduated-scale cylinder causes these appparent short lines to indicator of the kind in which a long graduated move both along the length of the window and scale is so mounted, relatively to a cursor line, across the width thereof. The window is closed that in adjusting the scale relatively to the said by means of a transparent covering it, which may cursor line the scale moves across the cursor line be flat but preferably, and as shown in Figure 2, and als along the length of the cursor line so is curved so as to conform with the shape of the that successive graduation marks are read cylinder. Traced upon this transparent cover is against successive points in the length of the a correction curve cc which is obtained by calcurson line, is characterised in this, that the ibrating the receiver at a suitable number of cursor line is fixed and is curved or shaped in acpoints on the scale. The cylinder is geared to cordance with ascertained errors, so as to correct the tuning handle of the radio-receiver through for such errors. a gear train (not shown) so that it may make a The rre ti n u s n line may be t a d upon number of revolutions to one complete cycle of a transparent cover with which the viewing winadjustment of the tuning member, the number dow is provided, or it may be cut in a thin sheet of revolutions depending upon the number of of opaque material (for example metal) the gradconvolutions of the scale line 8. Also geared with uation marks in either case being read at the the tuning handle, or, as shown, to the axle of point of intersection of the graduated scale line the cylinder is a pointer p so mounted relativeand correction cursor line. ly to the window, that for one complete cycle of Where the graduated scale line is traced several adjustment of the tuning member, the pointer times around a cylinder, or as a spiral of several makes one complete traverse of the length pf the window, being thereby always associated with the (apparent) individual line of the scale appropriate to the adjustment temporarily in being.

The calibration or correction cursor line cc is obtained in the following manner. In the shown position of adjustment of the receiver tuning means, as indicated by the pointer P (Fig. 3), the known received frequency as indicated by the graduation on the scale S is f1. The point a: on the transparent cover t that coincides with the scale graduation 11 determines the point on the curve cc to which the scale S must be moved at future times in order to adjust the receiver to the frequency f1 with precision. Similarly, the tuning means will be adjusted to other known frequencies f2, f3 and others, throughout its range, and the corresponding points 2, etc. are then marked on the transparent cover t, the curve cc representing the locus of all points thus obtained.

There may be, if the scale is used in connection with a radio-receiver serving a plurality of ranges, a like plurality of pointers p, p, 12", Figure 4, each pointer operating over an appropriate section of the scale, and each made operative as by illumination either of itself, or of the section of the scale, as the range of the receiver is changed. In Figure 4, which relates to such an arrangement, the reading is 8,430,000 c./s. (or 8.430 mc./s.).

The invention is of particular value when employed in connection with a self-calibrating radioreceiver.

Such a radio receiver, for instance a superheterodyne receiver, is provided with a local oscillator the frequency of which is of a high degree of constancy, and which has been adjusted to a predetermined value. As is usually the case in such oscillators, there are associated with the fundamental frequency a large number of barmonies which will, of course, be of known frequencies. One such receiver circuit is described in provisional specification No. 6744/41. The fundamental frequency of a local oscillator or a harmonic frequency is coupled to the input circuit of the receiver and induces signals therein. The receiver circuits are then tuned to this frequency. The point on the calibration scale corresponding to the known frequency of the induced oscillations gives one point on the correction cursor-line, and by repeating the process with the other harmonic frequencies the complete correction curve may be traced.

The positions on the scale corresponding to these frequencies may be marked in a distinctive manner so that a check on the constancy of calibration can be made by setting them against the cursor mark and noting whether the tuning is correct. The receiver may be provided with trimmer condensers to correct for any errors of tuning thus found.

The invention is also of particular value when employed in connection with a self-checking receiver, for instance of the superheterodyne type. Such a receiver is provided with a local oscillator constructed to have a frequency of oscillation which is maintained constant within narrow limits and of predetermined frequency. In addition to the fundamental frequency this local oscillator generates a large number of harmonic multiples thereof which fall upon points of the calibration of the receiver.

It is not thought to be necessary to describe in any detail, the manner in which the invention may be applied to a spiral scale on a disc. The correction cursor line, of course, in this arrangement will have a direction generally radially of the disc which will be mounted for rotation about the centre of the spiral line. A pointer may be provided in this arrangement also.

A band type indicator is so generally similar to a cylinder type that it is not thought necessary to describe the manner of its construction.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

1. In a visual indicator for radio apparatus the combination of a panel having an elongated viewing window, a transparent cover plate for said window fixed in position and provided with a correction cursor line extending lengthwise of said window, and a rotatable cylindrical member having a graduated scale line traced several times around its cylindrical surface, said scale line appearing through the viewing window as a plurality of substantially parallel lines which are arranged transversely of the cursor lineand intersect the latter at precise frequency adjustments of the radio apparatus.

2. In a visual indicator for radio apparatus the combination of a panel having an elongated viewing window, a transparent cover plate for said window fixed in position and provided with a correction cursor line extending lengthwise of said window, a rotatable cylindrical member having a graduated scale line traced several times around its cylindrical surface, said scale line appearing through the viewing window as a plurality of substantially parallel lines which are arranged transversely of the cursor line and intersect the latter at precise frequency adjustments of the radio apparatus, and a pointer movable lengthwise of the cylindrical member and in synchronism therewith for indicating on which of the parallel lines the precis frequency adjustment of the apparatus is being made.

CHRISTOPHER SYDNEY COCKERELL. 

